Cook pasta according to package directions, for the least amount of time shown. For example, if instructions say cook 7 to 10 minutes, cook for 7 minutes (the pasta will continue to cook in the oven). Drain, rinse, and set aside.
Meanwhile, shred the cheddar cheese and cube the cream cheese. If sweet potatoes are chilled, bring to room temperature.
Preheat oven to 375°.
Melt butter in a large sauce pan over medium heat. Add coconut milk and heat until it’s steaming and almost reaches a boil, stirring frequently.
Stir in cheddar, a handful at a time, stirring constantly. Repeat with cream cheese, a few cubes at a time, stirring constantly while the cream cheese incorporates. Add in mashed sweet potatoes and salt, and stir until the sauce is well blended. Turn off heat.
Pour half the sauce in a casserole dish. Add pasta and cover with remaining sauce. Sprinkle generously with breadcrumbs.
Bake for 20 to 25 minutes, until sauce is bubbling. Allow to cool 10 minutes before serving.